This invention relates to chrome-magnesite refractories and more particularly to chrome-magnesite refractories that have a controlled chemistry that makes them particularly resistant to siliceous slags. In the broad aspect, this invention relates to the control of the ratio of the oxide of chromium to the oxides of iron and aluminum, the total iron oxide, and silica content of the refractory, and the ratio between the chromite and the magnesia.
It is well known that numerous patents have been granted on various compositions of burned chrome ore and magnesite. Several of the earliest patents in this field that covered brick with a high percentage of chrome ore are U.S. Pat. Nos. 1,845,968 and 2,053,146. Brick in U.S. Pat. No. 2,077,796, were made with high silica content to form forsterite to bond the chrome ore and magnesite, while U.S. Pat. No. 2,270,220 discloses the use of dicalcium silicate to bond chrome ore and magnesite.
Since these early developments of chrome-magnesite refractories, there have been numerous changes in metallurgical practices, which typically operate at higher temperatures in the presence of highly corrosive slags. With this progress and improvement in the metallurgical industry, where chrome-magnesite brick are often used, there has been concomitant progress in the refractory art. Rebonded fused chrome-magnesite brick compositions as well as chrome-magnesite brick with fine chromic oxide additions, as described in U.S. Pat. No. 3,192,058, have been developed. These compositions have improved slag resistance, but they are substantially more expensive than conventional chrome-magnesite brick.
Accordingly, an object of this invention is a chrome-magnesite composition having high resistance to siliceous slags as occur in the copper industry, particularly those that occur in copper converters.
It is still a further object of this invention to provide a method for producing a burned refractory where the principal phases are chrome ore and magnesite, with control of the ratio of the chromium oxide to the oxides of iron and aluminum without the addition of chromic oxide, and also with control of the total iron oxide, and silica content and the ratio between the chromite and magnesia.
According to this invention, burned brick are made from a size graded batch comprising 20-30 weight percent magnesite containing less than 0.8 weight percent silica, and the balance a chrome ore whose ratio between the oxides of chromium and the oxides of aluminum and iron is greater than 2 to 1, the silica content of the ore is less than 2.7 weight percent, the iron oxide content is less than 17 weight percent, and the chrome ore to magnesite ratio is between 2.33 to 4 to 1.